Hybrid drives with internal combustion engine and electric motor drive sources contribute to the reduction of fuel consumption and polluting emissions in automobile traffic. In order to obtain the most effective and efficient operation of a hybrid drive, drive strategies are used that can flexibly utilize the electric machine of the hybrid drive depending on the situation. The electric machine is to be used as the sole drive source in the case of startup for example, in city short-haul traffic, or in stop-and-go operation, as an additional drive source in the case of increased power demands in a boost operation, as a starter generator for fast starts of the internal combustion engine and as a generator for generating electrical current, or for energy recovery in a recuperation operation. In contrast, the internal combustion engine is to be operated at least predominantly at operating points that are favorable for consumption, torque and speed with high efficiency.
In vehicle drive trains, hybrid drive arrangements are frequently combined with automated vehicle transmissions for forming drive transmission ratios. In doing so, hybrid drives, with which the electric drive and the internal combustion engine can be coupled to the drive train independently of each other, at least for individual transmission ratio steps, have advantages due to more flexible control thereof in comparison to arrangements with which the electric drive is permanently connected to the drive at the transmission input or at the transmission drive, that is, in the power flow of the drive train. With such hybrid drives, during shift procedures with the internal combustion engine, that is, gear changes while the internal combustion engine serves a drive source of the vehicle, the tractive force can be largely maintained with the aid of the electric drive. Conversely, during gear changes of the electric drive, the tractive force can be maintained with the aid of the internal combustion engine, insofar as the internal combustion engine is not currently switched off.
The shift procedures can be synchronized using the internal combustion engine and a friction engaged clutch acting between the internal combustion engine and the transmission input, and/or using the electric drive, so that synchronization devices can be replaced, at least to some extent, by more cost effective claw clutches. The shifting points with electric shifts, thus shifts occurring during the electric motor drive, can be basically very variably selectable due to the typically greater speed range available, with good efficiency compared to the internal combustion engine. Additionally, the attainable shifting times allow the use of a relatively inexpensive shift actuating system. Because an electric machine can basically be operated in both directions of rotation, by using a controllable reversal of the direction of rotation, it is possible to eliminate a separate reverse gear set. Additionally, the step changes of the internal combustion engine gears in such a hybrid drive system can be selected to be relatively large, whereby a relatively small number of gears can be used for implementing a specified overall gear ratio spread.
Such drive concepts have already been proposed for vehicles with which the electric drive is designed so that the electric drive alone has sufficient driving performance at least for a short-haul operation, in city traffic for example. These are so-called plug-in hybrid vehicles or range extender electric vehicles, with which an electric energy store is additionally externally chargeable and/or the internal combustion engine serves mainly for increasing the range and for generating energy for the electric drive.
Such hybrid drives with a manual transmission, which has two input shafts and a common output shaft, are known, wherein the output shaft is disposed in countershaft design and axis parallel to the input shafts. The one input shaft can be driven via an internal combustion engine, and the other input shaft can be driven via an electric machine. Both input shafts can be shifted, via gear sets coupled to the output shaft, and can be combined in a drive connection.
The unpublished document DE 10 2010 030 567 A1 describes such a hybrid drive with which two input shafts are disposed coaxially and axially adjacent to each other, and a common output shaft is disposed axis parallel to the input shafts. One of the two input shafts is separated into an axially outer and an axially inner shaft section. The outer shaft section is drive connected, or can be, drive connected to an associated internal combustion engine or to an associated electric machine. The inner shaft section supports gear sets assigned to the drive gears. Additionally, a superposition transmission is preferably provided as a planetary gear set having a sun gear and a ring gear as an input elements and a planet carrier as an output element. The input elements are each connected in a rotationally fixed manner to one of the two shaft sections. The output element is connected, or can be connected, in a rotationally fixed manner to the drive gear of an assigned startup gear set. A lock-up clutch, by means of which the superposition transmission can be locked, is disposed between the planet carrier and the ring gear.
This hybrid drive, in the case of an active superposition transmission, with an internal combustion engine drive that is running and connected to the respective input shaft, with the input shafts coupled together and an engaged start-up gear wheel set under the control of the electric machine from generator operation into motor operation, allows a wear-free startup with high tractive force, whereby a conventional friction clutch is not necessary as a start-up element. This function corresponds to the start-up function of comparable known electro-dynamic start-up elements, as described for example in the document DE 199 34 696 A1. This document shows one such wear-free electro-dynamic start-up element, with which a planetary gear set is disposed between the internal combustion engine and the transmission input, wherein a planet carrier is connected to a manual transmission, a ring gear is connected to the internal combustion engine, and a sun gear is connected to an electric machine. On the other hand, a hybrid drive according to the document DE 10 2010 030 567 A1 can be operated with an engaged lock-up clutch such as a hybrid drive with two input shafts and one common output shaft without a superposition transmission. A suitable basic hybrid drive with a three speed manual transmission with spur gears in countershaft design, with which two pure electric motor drive gears and three internal combustion engine drive gears and a boost operation, a recuperation operation and a charge operation can be selected, is also described in this unpublished document.
The document DE 10 2010 030 573 A1, also unpublished, also shows a comparable basic hybrid drive. Two input shafts are disposed coaxially over one another in sections, wherein the one input shaft assigned to the internal combustion engine is the inner shaft, and the shaft assigned to the electric machine is the outer shaft. A common output shaft is disposed axis parallel to the input shafts. A second electric machine is disposed on the input shaft assigned to the internal combustion engine. A friction clutch, by means of which the drive shaft of the internal combustion engine which could be connected, switchable to the respective transmission input shaft, is eliminated.